Background:
Cardiac
pacemakers and implantable defibrillators are potentially susceptible
to
electromagnetic interferences as they have complex circuitry for
sensing
and communication purposes. Cellular telephones being an important
source
of electromagnetic waves are likely to cause interference in the
function
of these devices.Methods:
A systematic analysis of studies on interaction between cellular
telephones
and implantable devices was done using professional databases for
literature.
Related articles and references of relevant articles were also searched
for
suitable studies.Results:
Fourteen studies on pacemakers and eight studies on implantable
defibrillators
were identified. No dangerous malfunction was found in any of the
analyzed
studies, but most of the studies noted interference with device
function
when the phone was operated very close to the device. Interference was
minimally
in those devices with built in feed-through filters for eliminating
electromagnetic
interference. Device programming and interrogation were the most
susceptible
phases of operation.Summary: Cellular
phones are likely to interfere with implantable rhythm devices if
operated
in close proximity or during programming of the device. Patients with
implanted
devices can safely use cellular phones if they are not carried close to
the
implanted devices or operated near them. Carrying the cellular phones
in
the belt position, receiving calls in the ear opposite to the side of
the
implanted device and keeping the phone as far away as possible while
dialing
can be considered a safe practice. Interrogation of the devices should
take
place exclusively in areas where utilization of cellular phones is
strictly
prohibited. Studies on pacemakers published in the current decade have
shown
much lesser rates of interference, possibly due to improvement in
device technology.

Implantable
rhythm
device (IRD) is the generic name for the group of implantable devices
used
for treatment of cardiac arrhythmias like cardiac pacemakers and
implantable
cardioverter defibrillators. Since these devices have complex
microelectronic
circuitry and use electromagnetic waves for communication with
programmers,
they are susceptible to interference from most sources of
electromagnetic
radiation and magnetic energy1.
Cellular telephones use radio frequency waves for communication and are
likely to interfere with the function of implantable rhythm devices.
Cellular telephones produce both static and dynamic
electromagnetic
fields. The magnet in the earpiece of the phone produces a low energy
static
magnetic field. This static magnetic field can activate the internal
reed
switch causing temporary suspension of sensing function when placed in
close
proximity to the implanted device2.
Dynamic fields with much higher intensity are produced by the radio
frequency
energy used for communication. Today we have two basically different
communication systems, analogue and digital systems that vary in their
ability to produce
interference with IRDs.

Methods

We
carried
out a systematic analysis of available data on the interference of
implantable
rhythm devices by cellular telephones. Database searches were conducted
using
the search words "cell phone, mobile phone, cellular telephone" in
combination
with "pacemaker, implantable cardioverter defibrillator, ICD" and
independently.
The retrieved results were checked to identify relevant studies.
Further
studies were sought by searching for the related articles and the
references
of the retrieved articles. Only clinical studies were included.

Studies Identified

The studies
identified
are listed in Table 13-24. The earliest
published
study dates back to 1995 and the latest was published in 2004. The
largest
study till date was done by Hayes et al, (1997) with 980 patients with
implanted
pacemakers11. The largest
study
on patients with implantable defibrillators (ICD) was published in 2002
with
97 patients19. A total of
14
studies on patients with implanted pacemakers and 8 studies on patients
with
ICD were identified3-24.
Interestingly, majority of the studies were from Europe, with only two
from
North America and one each from Asia and Australia. There were a total
of
3054 patients in all studies taken together.

Various types
of
analogue and digital cellular phones are in use across the globe.
Analogue
telephones transmit by modulation of the amplitude or frequency of
electromagnetic
waves which are transmitted continuously. On the other hand, the
digital
telephones transmit data in series of pulses or fast bursts. The
advantage
of the digital systems is that they allow simultaneous transmission of
messages
of different users on the same frequency which increases the capacity
of
the transmission channels. Digital phones are more likely to interfere
with
IRDs than analogue phones. This is because the pulse repetition rate of
the devices falls within the frequency range of physiological signals.
Different
frequencies
and technologies are in use in different parts of the globe. European
system
is GSM (Global System for Mobile Communications) in three different
frequency
ranges. The digital D-net works on a carrier frequency of 900 MHz and
the
digital E-net works on a carrier frequency of 1800 MHz. The C-net
working
analogue on 450 MHz was being used in European countries earlier25. GSM networks are in use in Asia and
Australia1,7.
The NADC-phones (North
American Digital Cellular) work on a carrier frequency of 835 MHz2.

Feed Through Filters

Feed
through filters are broadband filters using ceramic capacitors which
reduce
the influence arising from radio frequency sources on pacemakers and
ICDs
significantly. All IRDs have a titanium can which acts as an
electromagnetic
shield and a hermetic barrier to protect the internal components from
body
fluids. The lead wires which carry the pacing pulses and sense cardiac
activity
may also act as an antenna that conducts undesirable radio frequency
signals
from cellular phones to sensitive internal electronic circuits. The EMI
filter
decouples and shields such signals and prevents them from interfering
with
pacemaker or ICD functions.

Interference With Pacemakers

Until now,
pacemakers
constitute the large majority of IRDs and hence most of the studies
have
been on these devices. Of the 2726 patients included in the various
studies,
393 (14.4%) had some form of electromagnetic interference, when the
cellular
phones were operated in close proximity of the device. But there was
considerable
heterogeneity between the studies, with the percentage varying from 0
to
43. Inhibition of ventricular output, tracking of the interference
sensed
in the atrial channel and asynchronous pacing were the common problems
noted. Interference could be reduced by programming to lower
sensitivity levels5,15.
Increasing the transmitting
power of the cellular phone also increases the probability for
interference5. In the
practical scenario, this occurs in
rural areas where access points for the GSM phones are farther apart
and
the cellular phone automatically steps up the output. The studies
uniformly
reported no interference when the phone was held in the phoning
position
over the ear. Almost all the interferences occurred with the phone held
directly
over the device.
Pacemaker
interference
by cellular phones has been classified into three groups according to
the
clinical significance (Hayes et al11):

In this study, 20% of the total 5533 tests carried out showed
interference
of some form. Of these 1.7% were Class I, 4.9% Class II and 13.4% Class
III
interference.
The earliest
series
in this review was by Barbaro et al3.
This study involved 101 patients with 43 pacemaker models from 11
manufacturers.
26 patients showed interference at minimum sensing thresholds, with the
phone
in direct contact with the patient's chest. Pulse inhibition (9.9%),
ventricular
triggering (19.5%) and asynchronous pacing (7.7%) were the common
interferences
noted. Maximum distance at which interference occurred was 10 cm with
the
pacemaker programmed at its minimum sensing threshold.
The study by
Hayes
et al11 involving 980
patients
with implanted pacemakers was the largest of the lot. It is a well
designed
study with five types of cellular phones (one analogue and four
digital).
The telephones were programmed to transmit full power, to mimic the
worst
case situation. Of a total of 5533 tests conducted, interference was
noted
in 20%, of which 7.2% were symptomatic. Clinically significant
interference
was seen in 6.6%. No significant interference was noted when the
telephone
was placed in the standard phone position over the ear. As expected,
interference
was much higher when the phone was placed near the pacemaker.
Dual-chamber pacemakers were more susceptible (25.3%) than
single-chamber pacemakers (6.8%;
P<0.001). Pacemakers with feed-through filters were less susceptible
to
EMI (0.4 to 0.8%) than those without such filters (28.9 to 55.8 %,
P=0.01).
Marked difference was noted in the incidence of EMI between analogue
and
digital phones (2.5% vs 23.7%, P=0.01). Interference was higher among
pacemaker
dependent patients (20.9%) than those who were not (15.2%). The most
common
types of interferences were tracking interference (14.2%), noise
reversion
or asynchronous pacing (7.3%) and ventricular inhibition (6.3%). Less
common
problems noted were atrial inhibition (2.3%), ventricular safety pacing
(1.8%), undersensing (0.9%) and rate-adaptive sensor-driven pacing
(0.3%). Palpitations
was the most common symptom (4.5%). Light headedness occurred in 1.2 %
and
pre-syncope in 0.2%. Pre-syncope occurred only in those patients who
were
pacemaker dependent.
Study by
Altamura
et al12 included 200
patients.
Interference was noted in 21.5 % with GSM phones and 17.5% with Total
Access
of Communication System (TACS) telephones. Interference was much more
common
during ringing than on/off phase (131 vs 26 episodes, P<0.0001).
Incidence
of interference increased with increasing sensitivity (106 at maximum
sensitivity
vs 51 at basal values; P<0.0001). The authors concluded that if
phones
were not carried close to the pacemaker, safety was not compromised.
Raden et al15 reported a study on 144 patients with
implanted
pacemakers (134 with single chamber and 10 with dual chamber). While 9
patients
(6.25%) had intermittent pacemaker inhibition at basal settings, 17
patients
(11.8%) showed inhibition on reprogramming to maximum sensitivity. The
tests
were conducted with the phone directly over the pacemaker site.
Hofgartner et
al8 reported on 104 patients
with 58 different
models of pacemakers. Interference was noted in 28 different pacemaker
types
(48.3%) spread over 43 patients (41.3%). Pacemaker inhibition, noise
reversion
and triggering of pacemaker mediated tachycardia were noted.
All the above
series
with 100 or more patients which reported rather high incidence of
interference
were from the last decade (Figure 1).
The four studies published in the current decade report a very low
incidence
of interference21-24.
Smaller studies in the last decade have also reported low incidence4,6. In 2002, Elshershari
et
al21 reported on 95
patients
with pacemakers from 6 different manufacturers. Testing was done with
two
models of GSM D-net phones. Only one instance of brief oversensing was
noted.

Figure 1: Percentage of EMI
in
Major Studies on Pacemakers

Hekmat et al,
(2004)22 observed
pacing inhibition in only
2 patients out of 100, with the phones placed directly above the
pacemaker
pocket. These inhibitions occurred at programmed sensitivity values of
less
than 0.5 mV and could be eliminated by reprogramming to 1.0 mV. Hence
they
recommended programming ventricular sensitivity to 2.0 mV or higher. A
change
of lead configuration from unipolar to bipolar did not eliminate the
interference.
All pacemakers in this study were equipped with feed-through filters.
All
evaluated models showed significant telemetric noise when the phone was
placed
near the programming head, sometimes even causing loss of telemetric
data.
Trigano et al,
(2005)24 noted interference
in 1.5% of 330 tests
performed in 158 patients. Interference was noted only during 5 tests
in
4 unprotected pacemaker models due to interaction with GSM mobile
phones.
No interference was noted in 12 other tests of identical pulse
generator
models. The GSM phones had a maximal power output of 2 W and were
operating
on a 900 MHz carrier frequency.
The largest
report
of the current decade from Tandogan et al23
included 679 patients. Interference was noted in 37 patients (5.5%).
Thirty-three
VVI-R pacemakers were converted to asynchronous mode and 3 were
inhibited.
One DDD-R pacemaker developed ventricular triggering. Interference was
more common when the lead polarity was unipolar (4.12% vs 1.40%,
p<0.01). These
interferences did not cause any symptoms and the pacemaker function
returned
to normal when the cell phone was removed away from the patient.
It is likely
that
better pacemaker technology, especially the use of feed-through filters
could
have contributed to the lower incidence of interference in the recent
studies.

Interference With Implantable
Cardioverter
Defibrillators

In
the
last two decades, ICDs are fast becoming universal arrhythmia
management
devices for prevention of SCD, especially after the publication of
MADIT
I and II results. We could identify 8 studies on the influence of
cellular
phones on ICDs, with a total of 328 patients. 92 patients (28.09%)
showed
some type of interference when the activated phone was placed over the
ICD.
Pseudo-oversensing18,
ventricular
triggering17, telemetry
noise16 and partial loss of
telemetry13 were the types
of interference noted. No
inadequate shock therapy was observed. As in the case of pacemakers,
interference
occurred mostly when the phone was held close to the implanted device.
Devices
were most vulnerable for interference during the time of interrogation
and
programming.
The largest
available
study was on 97 devices reported by Niehaus et al in 200219. D-net (900 MHz) and E-net (1800 MHz)
phones
were used for testing. Interferences (loss of communication or
temporary
inactivation of the device during interrogation) were noticed in 38
patients.
Most of these (93%) occurred while testing close to the device. Jimenez
et
al13 published in 1998
their
study on 72 patients of which 14 showed interference. Partial loss of
telemetry
was found in 8 patients with analogue phones and 6 patients with
digital
phones. But none of these were clinically significant.
Occhetta et al
(1999)16 reported on thirty
patients with ICDs from
five different manufacturers. Both TACS and GSM phones were used for
testing.
This study was unique in that it reported interference with all the
evaluated
models. The interference consisted of noise in telemetric transmission
when
the phone was located near the ICD and the programmer´s head. The
noise
was most significant during call and reception, leading to loss of
telemetry
in most cases.
It is
important
to note that there was no false arrhythmia detections during the tests,
neither
a delay in recognition of induced ventricular fibrillation. Hence they
suggested
that patients with implanted ICDs may use cellular phones, but not
during
ICD programming and interrogation. In contrast to the above report,
Fetter
et al14 who studied the
effect
of North American Digital Communications (NADC)/Time Division Multiple
Access-50-Hz
(TDMA-50) digital phones on ICDs, reported no interference due to
oversensing
of the dynamic electromagnetic field in their 41 patients. However,
they
found that the static magnetic field of the phone's earpiece placed
over
the ICD will activate the internal reed switch causing temporary
suspension
of ventricular tachycardia and fibrillation detection.
Chiladakis et
al18 reported on 36
patients with ICDs from two
manufacturers. In seven devices from one manufacturer, they noted
transient
EMI causing 19 erroneous sensing events (pseudo-oversensing) when the
phone
was operated close to the programmer head. But these events were not
logged
as arrhythmia episodes by the counter in the device. Therefore this
observation
has to be interpreted as adverse interaction between the phone and the
telemetry
function of the ICD. No interference in the function of the ICD was
documented
regardless of the distance, power or mode of operation of the cellular
phone.

ConclusionIn
summary,
cellular phones are likely to interfere with implantable rhythm devices
if
operated in close proximity or during programming of the device.
Patients
with implanted devices can safely use cellular phones if they are not
carried
close to the devices or operated near them. Carrying the cellular
phones
in the belt position, receiving calls in the ear opposite to the side
of
the implanted device and keeping the phone as far away as possible
while
dialing can be considered a safe practice. Interrogation of the devices
should
take place exclusively in areas where utilization of mobile
phones
is strictly prohibited as this is the period in which maximum
interference is likely. Due to the heterogenic reactions of the
implanted devices on cellular
phones, EMI by cellular phones should be tested carefully in every new
developed
implantable rhythm device.